I. Field of the Invention
This disclosure relates generally to systems, apparatus and methods for estimating a location of a mobile device, and more particularly to capturing and using only some RTT measurements while excluding other RTT measurements when computing a location estimate of the mobile device based on a feature of access points.
II. Background
In current high-precision indoor positioning, also known as precise indoor positioning (PIP), a mobile device measures round-trip time (RTT) between the mobile device and various assess points, estimates a turnaround calibration function (TCF) for each RTT measurement, computes a difference between each RTT measurement and the corresponding TCF, and then computes a position estimate of the mobile device based on the differences. A TCF for each access point introduces an uncertain value. A TCF includes the delays both within an access point (primarily due to short interframe space (SIFS)) and within the mobile device. For example, IEEE 802.11 systems may set a TCF based on the physical (PHY) layer and the operating frequency band of each access point.
It can be useful is a way to reduce a number of unknowns by grouping access points and generalizing a TCF value for a group before computing a location estimate based on a more accurate group while excluding less accurate groups of access points.